Modem callers

Modem callers reach the BBS through the D-Modem suite, in one of two ways: straight from the call through app_dmodem, D-Modem's Asterisk application, or through modemmenu after its login. This page covers both, how to give callers the same password everywhere, and how the BBS works out where callers are.

Straight from app_dmodem¶

app_dmodem's [bbs] profile hands each call to a TCP server as raw bytes. The sample's [listen modem] is that server:

; dmodem.conf
[bbs]
mode = tcp
host = 127.0.0.1
port = 2323

; bbs.conf
[listen modem]
type = raw
address = 127.0.0.1:2323

The caller then logs in to the BBS, or signs up. Over a raw line the BBS asks the terminal for its cursor position. An ANSI terminal (SyncTERM, Telix, Qmodem, HyperTerminal in ANSI mode) answers, and the answer also tells the BBS the screen size; any other terminal gets plain text. Text is 7-bit ASCII unless the caller turns UTF-8 on. If app_dmodem sends a session header (header = yes), the BBS learns the call's rate and caller ID; set header = yes on the listener too.

Behind modemmenu¶

modemmenu logs the caller in first and offers the BBS as an item in its menu. There are three ways for it to hand the caller over, from the simplest to the most closely linked.

rlogin is modemmenu's default for a BBS. It sends the caller's password as the rlogin client user and their name as the server user (Synchronet's convention). The BBS checks them against its own accounts. If they do not match (the user has no account on the BBS, or a different password), the caller is asked to log in, with their name already filled in.

; modemmenu.conf
[item bbs]
key = B
label = Bulletin board
mode = rlogin
host = 127.0.0.1
port = 2513
after = menu

; bbs.conf
[listen rlogin]
type = rlogin
address = 127.0.0.1:2513

A unix socket with the session header lets the BBS trust modemmenu's login (trust_user). Callers do not need an account on the BBS first: create_users = yes creates one for each new name. Such an account has no BBS password of its own; it logs in this way, or with the modemmenu password (described below). The rate, caller ID and number from the header appear in the log and in Who's online.

; modemmenu.conf
[item bbs]
key = B
label = Bulletin board
mode = unix
path = /run/bbs/menu.sock
header = yes
pass_password = no
after = menu

; bbs.conf
[listen menu]
type = raw
address = /run/bbs/menu.sock
header = yes
trust_user = yes
create_users = yes
socket_mode = 0660
socket_group = asterisk

trust_user trusts whoever can connect, so make sure only modemmenu's user can reach the socket (Asterisk's group with mode 0660, or mode 0600 and the same user). bbs check warns about a trusting socket or port that others can reach.

telnet works too (mode = telnet, port = 2300). modemmenu's telnet client says it is an ANSI terminal, and the caller logs in again.

The same password for telnet, SSH and the web¶

Accounts that modemmenu logs in have no password on the BBS. With modemmenu's auth socket, the same people can log in to the BBS any other way (telnet, SSH, TN3270, the web forum and terminal, the API, FTP, NNTP, IRC) with their modemmenu password. The BBS asks modemmenu, and modemmenu asks its own backends (its users file, LDAP, SQL, or the system's accounts through PAM), just as it does at its own login prompt. The BBS keeps nothing of the password.

; modemmenu.conf: answered by modemmenu -serve, or modemmenu -authd alone
[authd]
listen = /run/modemmenu/auth.sock
socket_mode = 0660
socket_group = bbs
allow_users = bbs

; bbs.conf
[modemmenu]
auth_socket = /run/modemmenu/auth.sock

The BBS asks modemmenu only about accounts modemmenu created (external accounts with no BBS password). An account with its own BBS password keeps it, and the modemmenu password does not open it. A wrong password counts as a failed login like any other (throttling, the hack log). If modemmenu does not answer, the caller is told there is a problem, and it is not counted against them. These passwords are changed in modemmenu (or its backend), not in the BBS.

Callers can also sign in without typing a password. While signed in on the BBS, the sign-in code in Your profile (C) signs in to the web forum once, within five minutes (see Web forum), and SSH keys added there (K) log in by SSH with no password.

Where callers are¶

With [general] phone_country set, the BBS reads modem callers' numbers using each country's numbering plan. From a number it learns:

• the country, even where countries share a calling code (Jersey and Britain, Kazakhstan and Russia, Jamaica and the US);
• what kind of number it is (fixed line, mobile, toll-free, premium rate, VoIP and so on);
• the place it is in, down to the exchange where the plan says (Jersey City, NJ, Ontario, London, Berlin, Tokyo; 151 calling codes have places).

International numbers (+44 20...) are read whatever phone_country is. National numbers, which is how exchanges mostly send them, are read the way that country dials, with its trunk and international prefixes removed (4155550123, 1 415 555 0123 and 011 44... with US; 020 7123 4567 and 00 1 415... with GB; 8 495 ... and 810 ... with RU). A local number without an area code gives only the country, and a withheld number gives nothing.

[general]
phone_country = US
;geoip = /var/lib/bbs/dbip-country-lite.mmdb   ; for callers by address

The log records this with each call, writing the number as it is written from abroad:

node 3: modem on [listen modem]: rate 33600/31200, from 4155550123 (+1 415-555-0123), in San Francisco, CA, United States
node 4: modem on [listen modem]: rate 26400/26400, from 08005550123 (+44 800 555 0123), in United Kingdom (toll-free)

Who's online shows each caller's country (from the caller ID, or else from their address with [general] geoip). The sysop's node list (spy, chat, kick) also shows their number, whether it is a mobile, and the place. Posts keep the poster's country for the web forum's flags.

By address: countries, regions and cities¶

Callers by telnet, SSH, the web terminal and the forum are placed by their address, using the database in [general] geoip. A country database gives a country. A city database also gives a region (state, province or county) and a city, which the log and the sysop's node list show (Mountain View, California, United States); Who's online, the API and the forum's flags still show only the country. Either kind works, in either format:

[general]
geoip = /var/lib/bbs/dbip-city-lite.mmdb
geoip_credit = IP geolocation by DB-IP
geoip_credit_url = https://db-ip.com

DB-IP's free city database is a monthly download (https://download.db-ip.com/free/dbip-city-lite-YYYY-MM.mmdb.gz, 60 MB), and it can stay gzipped. It takes about 120 MB of memory. Its CSV version (86 MB gzipped, 7.8 million ranges) takes 135 MB and about 15 seconds to read, while the .mmdb loads at once. The BBS reads the file when it starts, not at the first call. If you replace the file, it is read again in the background within a minute, and the old one answers meanwhile. The reader was checked against MaxMind's own reader on DB-IP's city database of October 2026, in both formats, and gave the same country, region and city for 200,000 addresses. The image boards' flags use the same file (loaded once) unless [chan] geoip says otherwise.

The numbering plans come from Google's libphonenumber (Apache License 2.0), and North America's area codes from NANPA's own area code report. An area code NANPA has in service is recognised even where libphonenumber has not caught up, its state or province is taken from NANPA, and an area code announced for a later date starts working on that date. Both are built into the BBS, so nothing is looked up online. To rebuild the tables from newer data (internal/phone/gen):

git clone --depth 1 https://github.com/google/libphonenumber
curl -O https://reports.nanpa.com/public/npa_report.csv
make phone-data LIBPHONENUMBER=libphonenumber NANPA=npa_report.csv

The tables were last rebuilt in October 2026, from NANPA's report of 14 October and libphonenumber's data of 8 October (which was then missing thirteen area codes NANPA had in service). They were checked against libphonenumber's Go port (nyaruka/phonenumbers) on 34,000 numbers and gave the same country, kind and place for every one.

A modem call by VoIP without a caller ID¶

When a call has no caller ID, the BBS falls back to the address the call came from over VoIP, if the modem server tells it (DMODEM_PEER in the session header: 203.0.113.5, 203.0.113.5:5060 or sip:...@203.0.113.5 all work). The address is looked up in [general] geoip like any other. This is a best guess: a call that came in through a VoIP provider gives the provider's address, not the caller's.

New users, and users who share where they are¶

A new user's Where are you calling from? starts filled in with where their caller ID or address says they are (San Francisco, CA, United States, London, England, United Kingdom). They can change it or clear it. The web forum's sign-up form does the same. geoip_prefill = no turns this off.

New users are then asked whether the sysop may see where they call from. The answer is no unless they say yes, and they can change it at any time in their profile (Share where you are with the sysop), or through the API (PATCH /api/v1/me with share_location). For a user who says yes, the BBS keeps the place at each login, with how it was found (caller ID, address, VoIP address) and the date. Sysops see it on the user's page (in the user list, in the sysop's user editor and in bbs config) and in the API's geo. A user who stops sharing has what was kept forgotten at once. geoip_users = no stops asking, and stops keeping it. The question is only asked when there is a way to find the place (geoip or phone_country).

[general]
geoip_users = yes     ; ask users whether the sysop may see where they are
geoip_prefill = yes   ; fill in a new user's location

See also: Configuration, File transfers